Sen. Chuck Hagel, R-Neb. / Lauren Victoria Burke, AP

by David Jackson, Tom Vanden Brook and Aamer S. Madhani, USA TODAY

by David Jackson, Tom Vanden Brook and Aamer S. Madhani, USA TODAY

WASHINGTON -- President Obama's choice of former GOP senator Chuck Hagel to lead the Defense Department likely sets up a contentious nomination fight in the Senate.

Obama plans to nominate Hagel today to lead the Pentagon as Defense secretary, according to two officials familiar with the nomination process. Both officials spoke on condition of anonymity because it had not been officially announced.

Senate Minority Leader Mitch McConnell, R-Ky., declined Sunday to endorse his former Senate colleague, saying only that whoever is nominated will get a thorough vetting. "I'm going to take a look at all the things Chuck has said over the years," McConnell said on ABC's This Week. "I'm going to want to see how the hearings go."

Hagel, 66, served two terms in the Senate, representing Nebraska from 1997 to 2009. He led an Army infantry squad in Vietnam in 1968. He was wounded in action there and received two Purple Hearts.

Hagel, if approved by the Senate, would succeed Leon Panetta and would inherit a military frayed by more than a decade of war and facing at least $500 billion in spending reductions over the next decade. It is also shedding about 100,000 soldiers and Marines.

Since his name surfaced as a potential nominee, Hagel has come under criticism from some supporters of Israel and gay groups for comments he has made.

Hagel once referred to the "Jewish lobby" in reference to advocates for Israel who lobbied the Senate. In 1998, he referred to a nominee for ambassador in the Clinton administration as "aggressively gay."

Hagel said he misspoke about Israel's supporters and recently apologized for the comment about the gay nominee.Hagel has angered fellow Republicans. He voted to authorize President George W. Bush to use force in the run up to the Iraq War, but he later lamented the way the wars in Iraq and Afghanistan were fought.

Some Republicans, including Arizona Sen. John McCain, said Hagel has been too critical of Israel and too soft on Iran and its nuclear program.

Sen. Lindsey Graham, R-S.C., said on CNN that he likes Hagel personally, but he is "out of the mainstream" on foreign policy views, and his nomination would be "antagonistic."

"This is an in-your-face nomination by the president," Graham said. "This is a controversial pick."

Sen. Dick Durbin, D-Ill., the Senate's number two Democrat, noted that Hagel is a Republican, a decorated combat veteran who served in Vietnam, and has vast foreign policy experience. Speaking on CNN's State of the Union, Durbin also pointed out that Obama won the presidential election, and is entitled to name his team. "Yes, (Hagel) is a serious candidate," Durbin said.

In an interview on NBC's Meet the Press a week ago, Obama praised Hagel as "a patriot. He is somebody who has done extraordinary work both in the United States Senate, somebody who served this country with valor in Vietnam. And is somebody who's currently serving on my intelligence advisory board and doing an outstanding job."

In response to criticism from gay groups, Obama noted Hagel's recent apology for his comment about the ambassador nominee.

Hagel would face immediate decisions on Pentagon issues. The pace of the withdrawal of troops from Afghanistan - all U.S. forces are scheduled to depart by 2014 - will be at the top of the list. There are about 66,000 U.S. troops there now, and commanders would like to keep as many as possible through next summer, when fighting peaks.